Attached is an application note from ADI.
Would like to know the recommended layout for page 15 of the document and its component package/details.
For the circuit on Figure 29, we used EVBs of the bias controller and the amplifier, BOM on their datasheets can be used as reference.
The bypass CAP count on bias pins is reduced on the amp EVB, these are for PSU filtering basically you can use other combinations. REfer to Q2 on the following FAQ,
FAQ on Hittite Microwave RF/MW Amplifiers from ADI
We used 0603 packaged resistors for R20, R22 and the resistors on the Vgg2 pin, 0402 parts can also be used.
Top up to the previous question:
1) R20 and R22 and Rsense. Any particular tolerance or temp coef required?
2) Can the tantalum caps on both amplifier and biasing IC be replaced with ceramic (X7R) 1206 package caps. Will this affect performance?
3) Is the amplifier sensitive to stray capacitance and inductance due to layout and cause the amplifier to be unstable?
1. There are no requirement on the tolerance on all3 resistors. However Rsense sets the drain current for the DUT, so any variation on its value either due to part to part or process will affect the Idd for the DUT. If your application requirements can handle the variation of the resistor, then you do not need to worry about how high performance the resistor is. If you want to stay in lower variation limits for Idd, then resistors with 1 percent tolerance can be used.
For R20 and R22, please refer to `ADJUSTING THE DEFAULT VNEG AND VGATE THRESHOLD VALUES` section of the app note. Especially last paragraph gives idea on how to approach these resistor values. It is improtant to make sure the Vneg threshold is below Vgate threshold. To use an even safer design approach R20 and R22 can be chosen different to avoid part to part variations on the resistors.
2. Bypass caps are required for power supply filtering, so they can be replaced with ceramic ones. We have not tested the circuit by replacing tantals with ceramics, but unless otherwise stated in the app note or datasheets you can replace tantals with ceramic capacitors. An example cap where the usage of tantalum capacitors is suggested can be found on the pin description table for pin 29 on the HMC920LP5E datasheet.
3. RF devices are usually sensitive to the stray capacitance and the inductance. Especially high ground inductance introduced due to poor layout techniques can result in low performance or instability. Following the layout given on the datasheet EVB drawing section will help to get datasheet performance. More details can be found on the gerber files provided on the product page.
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